Arrangement for coupling a parallel resonant line to a coaxial line load



Dec. 26, 1950 STEIGERWALT 2,535,329

ARALLEL RESONANT ARRANGEMENT COUPLING A P LINE TO A COAXIAL L LOAD Filed March 26, 6

INVENTOR OLIVER I. STEIGERWALT ATTORNEY Patented Dec. 26, 1950 ARRANGEMENT FOR COUPLING A PARAL- LEL RESONANT LINE TO A COAXIAL LINE LOAD Oliver I. Steigerwalt, Niagara Falls, N. ;Y., assignor to United States of America as represented by the Secretary of War Application March 26, 1946, Serial No. 657,300

3 Claims. 1

This invention relates to resonant circuits and more particularly to a structure providing coupling between a load and a resonant parallel line circuit.

It is frequently desirable in high-frequency circuits to utilize a parallel line as the resonant circuit. of an oscillator, and it is often desirable to couple a low impedance load to the line. This invention provides simple means for placing the load effectively in series with the resonant line to provide a transfer of energy to the load, particularly where the load includes a coaxial cable termination, and. simultaneously affords means for adjustment of the electrical length of the resonant line. I

Therefore, among the objects of the invention is to provide a means for coupling a coaxial cable terminating load to a resonant parallel line circuit; to provide such coupling while still permitting tuning of the resonant line circuit; and to provide such a coupling in which the load is effectively in series with a resonant parallel line. of adjustable length.

Other objects, advantages, and novel features of the invention will be apparent from the description herein, wherein reference is made to the single figure of the accompanying drawing illustrating a preferred embodiment of the invention.

Referring now to the drawing, tubular conductors 5 and 6 act. as a tuned parallel line leading to the anodes of a split-anod magnetron l to provide a resonant circuit. In the embodiment shown, line 5 extends through and beyond a slidable plate 8 to form the inner conductor 9 of a coaxial line H), and line 6 is electrically connected to the outer conductor of coaxial line [0, so that the coaxial line may be considered to be in series with the parallel resonant line circuit.

Lines 5 and 6 extend through apertures in the slidable metallic plate 8, and sliding electrical contact between the plate 8 and line 6 is provided by finger elements [5 mounted upon plate 8. Plate 8 is further mechanically and electrically connected to a section of coaxial tubing [6, which extends about the inner conductor 9 adjoining line 5. The section of coaxial tubing I6 telescopes into and is electrically connected to a stationary outer conductor ll of coaxial line ID. The coaxial line inner conductor 9 formed by the extension of line 5 is likewise tubular in structure. An insulating annular dielectric ring 18 which is fastened to the inner surface of coaxial tubing l6 serves to space line 5 within an aperture of plate 8 and to insulate the line 5 and its extension 9 from the section of coaxial tubing [6 which extends through said aperture. Dielectric ring [8 further furnishes physical support to the inner conductor 9 to maintain the spaced rela tionship necessary in coaxial line 10. A box-like metallic shield l9, here shown with certain sides removed to expose the inner structure to view, may be provided around the magnetron 1 and parallel lines 5 and 6 to prevent undesired radiation of energy and also to serve as a mount for the tube and parallel line structure. Slidable plate 8 may be further provided with finger elements 20 to contact the inner surfaces of the boxlike shield [9 as shown. A worm 2| is mounted to extend perpendicularly to slidable plate 8 and to be actuated by a drive handle 22, so that engagement of Worm 2| with a cooperating element (not shown) on metallic plate 8 will serve to adjust the efiective lengths of lines 5 and 6 by positioning plate 8 along the parallel line. Telescoping section H; of the outer conductor of coaxial line l0 may thus be advanced within or withdrawn from stationary outer conductor H with movement of plate 8. Telescoping section [B is provided with finger elements 23 contacting the inner surface of stationary outer conductor ll into which telescoping section [6 extends. The outer conductor of coaxial line H! is thus continuous from slidable plate 8, and variable in length. The length of coaxial line I0 is thus increased as the effective length of the tunedparallel line is decreased, and vice versa. The coaxial line H) is formed into a U-shape having two substantially parallel legs as shown. The telescoping leg of the U-shaped coaxial line is formed by the inner conductor 9 and the telescoping sections I 6 and IT as described, and the other leg 24 includes a series of transformer sections. The inner conductors of the transformer sections have decreasing diameters as shown, and the length of each section is one-quarter wavelength at the mid-frequency of the operating frequency band. An impedance matching structure is thus provided which is relatively insensitive to frequency changes. Leg 24 of coaxial line H] leads to an output terminal 25 for connecting to a conventional low impedance coaxial line. A conventional quarter-wavelength stub 26 may be provided as shown in the arm connecting the two legs of the coaxial line. The inner conductor 24 of this stub 26 may be formed as a hollow tube connecting to the hollow inner conductor 9 of coaxial line I0. A coolant may thus be carried by the hollowed inner conductor of the coaxial line, to the tubular lines 5 and 6 which communicate with suitable cooling structure within the magnetron 7. The line 6 is for this purpose further provided with a connecting tube 30 to complete the cooling circuit.

That part of the coaxial line along which tubing l6 moves may be designed to have a varying impedance along its length so that the impedance presented to the oscillator circuit by the load is a chosen function of the operating frequency. This diametral variation may serve to maintain the desired degree of coupling over the operating frequency band. The characteristic impedance of th coaxial line leg formed by the telescoping sections l6 and I! may be designed to be lower than the characteristic impedance of the load to be connected to terminal 25. In the preferred embodiment, this leg is approximately one-fourth wavelength long at the lowest. operating frequency at which plate 8 is fully advanced to maximize the length of lines 5 and 6. At the highest frequency, when plate 8 is retracted to make the effective length of lines 5 and 6 a minimum, the telescoping leg of the coaxial line is approximately one-half wavelength long.

The conductance presented to lines 5 and 6 at their effective junction with the coaxial line 9, l0 varies between substantially at the lowest frequency and at the highest frequency, where BL is the impedance presented by the load and connecting coaxial line to the telescoping section I7, and Rx isthe characteristic impedance of the telescoping leg [5, ll. The conductance presented to the resonant line circuit at plate 8 is transformed by resonant lines 5 and 6 to a suitable conductance .at magnetron l for its proper operation.

It will be apparent to those skilled in the art that many variations of the invention are possible. As one example, other tubes than a magnetron oscillator could be used. Therefore, it is not desired to restrict the invention to the precise embodiment herein disclosed.

What is claimed is:

1. A resonant parallel line and load coupling structure, including two parallel resonant lines, a movable metallic plate having two apertures through which said lines extend, metallic members extending from said plate and providing contact with one of said lines, an annular dielectric member about the other of said lines insulating and spacing said other line within one said aperture, an inner coaxial conductor connected to and constituting a continuation of said other line, a section of coaxial tubing attached to said plate and extending about a portion of said inner co- 4 axial conductor, a quarter wavelength stationary outer coaxial conductor extending about said section of coaxial tubing and said inner coaxial conductor, sliding contact means between said section of coaxial tubing and said outer coaxial conductor, and a coaxial transformer section electrically. connected at one end to said outer and inner coaxial conductors and adapted at its other end to be connected to a load.

2. A resonant parallel line and load coupling structure, including two parallel resonant lines,

a movabl metallic plate having two apertures through which said lines extend, metallic members extending from said plate and providing contact with one of said lines, adielectric member insulating and spacing the other of said lines within one said aperture, an inner coaxial conductor connected to and constituting a continuation of said other line, a section of coaxial tubing attached to said plate and extending about a portion of said inner coaxial conductor, a stationary outer coaxial conductor extending about said section of coaxial tubing and said inner coaxial conductor, and sliding contact means between said section of coaxial tubing and said outer coaxial conductor, said outer and inner coaxial conductors being adapted for connection to a load.

3. A resonant parallel line and load coupling structure, including two parallel resonant lines, a movable metallic member having sliding contact means to electrically connect said member with one of said lines, a dielectric member insulating and spacing said movable metallic member from the other of said lines, an inner coaxial conductor connected to and constituting a continuation of said other line, a section of coaxial tubing attached to said plate and extendin about a portion of said inner coaxial conductor, a stationary outer coaxial conductor extending about said section of coaxial tubing and said inner coaxial conductor, and sliding contact means between said section of coaxial tubing and said outer coaxial conductor, said outer and inner c0- axial conductors being adapted for connection to a load.

OLIVER I. STEIGERWALT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Radar School (page 7-48), Chapter VII, Technology Press, 1944.

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